The invention relates to a dispensing device for comminuting a liquid and the uses of such a device, especially in medicine.
1. Background
Dispensing devices are known which produce a finely divided spray of liquid droplets by electrostatic (more properly referred to as xe2x80x98electrohydrodynamicxe2x80x99) means. The droplet spray in such devices is generated by the application of an electric field to a liquid at a spray head or spray edge. The potential of the applied electric field is sufficiently high to provide comminution of the liquid from the spray head. The droplets produced are electrically charged and thus are prevented from coagulating by mutual repulsion.
Electrohydrodynamic sprayers have potential uses in many areas, including agriculture and the automotive industry and also for dispensing cosmetics and medicines.
2. Prior Art
United Kingdom patent number 1569707 describes such an electrohydrodynamic spray device principally for use in crop spraying.
United Kingdom patent number 2018627B discloses an electrohydrodynamic spray device wherein the charged droplet spray is fully or partially electrically discharged by means of an earthed electrode having a sharp or pointed edge and located downstream of the spray head. European Patent number 0234842 also uses this technology and relates to an inhaler in which charged droplet spray is discharged prior to inhalation by means of a sharp or pointed discharge electrode carrying an opposite charge to the droplet spray and located downstream of the spray head. The droplets are discharged to facilitate droplet deposition into the respiratory tract by preventing deposition of charged droplets onto the mouth and throat of the user.
A common feature of all known electrohydrodynamic spray devices is that the electric charge used to generate the spray is applied directly to the spray head. It has now surprisingly been found that the direct application of the field is not essential and that the electrohydrodynamic comminution of a liquid may be accomplished by inducing the required electric charge at the spray head. In addition and advantageously, it has been found that the comminutions produced can be partially or fully discharged prior to use.
This method of induced charging has been found to provide better comminution of liquid having lower electrical resistivity.
Accordingly, it is one aspect of the invention that there is provided an electrohydrodynamic dispensing device for comminuting a liquid, wherein the liquid is comminuted by an induced electrical charge.
In yet a further aspect, the means for fully or partially discharging the liquid comminution is provided by an electrode arranged to have a first surface capable of producing an electric field sufficient to induce the required charge for liquid comminution in the comminution means and also to impart sufficient inertia to the liquid comminution so that is substantially bypasses the first surface, the electrode also having a second surface capable of producing an ionic discharge to fully or partially discharge the liquid comminution.
The dispensing device normally comprises a comminution site, a means for supplying liquid to the comminution site and a means for inducing an electrical charge at the comminution site sufficient to comminute the liquid.
The comminution site may be any conventional electrohydrodynamic comminution site such as a surface or edge generally provided by a thin capillary tube, a nozzle or a slot defined by two parallel plates.
Appropriate means for supplying liquid to the comminution site include mechanical or electrically powered pumps which are capable of providing the required flow rate of liquid to the comminution site which such as a syringe pump or the electrically powered pump described in EP 0029301.
The comminution means of the invention can be used with a large range of flow rates, but generally operates with flow rates in the range of between 0.1 to 500 xcexcL per second, such as 0.5 to 5 xcexcL per second, especially for inhaled administration, or 10 to 200 xcexcL per second, especially for agricultural use.
The means for inducing the electrical charge at the comminution site may be any conventional source of electrical charge which in use is capable of inducing a charge sufficient to comminute the liquid from the comminution means including a high voltage generator or a piezo-electric generator. The charge required is usually of the order of 1-20 kilovolts for example 10 kilovolts.
After formation of the liquid comminution, the electrically charged liquid droplets are attracted towards and will impact the means for inducing the electrical charge at the comminution site. In a preferred aspect of the present device, there is therefore provided a means for partially or fully electrically neutralizing the liquid comminution before it impacts the induced charging means.
One suitable means for partially or fully electrically discharging the liquid comminution is a sharp or pointed discharge electrode located downstream of the comminuted liquid.
The sharp or pointed discharge electrode may be earthed or it may be maintained at a polarity opposite to that of the induced charging means by connection to a suitable charging means. In either case the comminuted liquid is partially or fully discharged by a cloud of charged ions produced from the surrounding air having an opposite electrical charge to that on the comminuted liquid spray. The ion cloud is attracted towards, collides with and thereby partially or fully discharges the liquid spray.
In one particularly advantageous form of the device, the means for fully or partially discharging the liquid comminution is provided by a combination of the sharp or pointed discharge electrode and at least one capacitor, the capacitor acting to absorb the charge from the gaseous ions from the sharp or pointed discharge electrode until the induced comminution of the liquid is established, the capacitor is arranged to absorb the ions until is reaches a predetermined potential at which potential is ceases to absorb the ions thereby allowing them to partially or fully discharge the liquid comminution.
Generally, the capacitor is chose to have a time constant having the same order as the time required to establish the liquid comminution spray cloud. Thus the time constant will have a value, in seconds, which is the product of the capacitance, C and the resistance, R, of the capacitor.
The value of Cxc3x97R for the capacitor is chosen so that the capacitor will charge until it reaches a prearranged potential sufficient to modify the electric field, the capacitor then discharges towards the established spray cloud. Generally, the time-constant required will be of the order of seconds or a number of milliseconds. For example, a capacitor of 0.1 microfarad with a resistance of 10 megohms will produce a time constant of one second.
In yet a further aspect, the means for fully or partially discharging the liquid comminution is provided by an electrode arranged to have a first surface capable of producing an electric field sufficient to induce the required charge for liquid comminution in the comminution means and also to impart sufficient inertia to the liquid comminution so that it substantially bypasses the first surface, the electrode also having a second surface capable of producing an ionic discharge to fully or partially discharge the liquid comminution.
Generally, the second surface is shaped to have a sharp edge or a point which in use produces the ionic discharge.
Suitably, the electrode is an annular electrode coaxially located with respect to the intended flight path of the liquid comminution, in use the upper surface of the annular electrode induces the required charge in the comminution means, the lower surface being shaped so as to produce the ionic discharge.
In operation the field pattern of the upper surface of the annular electrode is such that the comminution is directed onto an axial flight path with respect to the annular electrode and is provided with sufficient inertial force to substantially bypass the first surface, the comminution is then fully or partially discharged by the gaseous ions produced by the second surface.
The device of the invention may be used to dispense liquids comprising components useful for human or animal health care, such as medicaments for pharmaceutical or public health care use of medically useful compounds such as anesthetics.
Suitable liquids include liquids comprising components for agricultural use such as pesticides or biocides.
Suitable liquids include liquid cosmetic formulations.
Other suitable liquids include paints and inks. Also included are liquid for providing aromas.
Preferred liquids are pharmaceutically active liquids.
The communition means of the dispenser provides liquids droplets within the range of from about 0.1 to about 500 microns in diameter. More usually from 0.1 to 200 microns, such as 1.0 to 200 microns: Examples include droplets within the range of 5.0 to 100, 0.1 to 25, 0.5 to 10 to 20 microns. A favoured range for inhaled administration is 0.1 to 25 or 0.5 to 10 microns, especially for administration to the lower respiratory tract, and 10 to 25 microns, especially for administration to the upper respiratory tract.
For a given liquid the diameter of the droplets can be controlled by varying the applied voltage and liquid flow rate using routine experimental procedures.
Liquids having viscosities within the range of from 1 to 500 centipoise and resistivities in the range of from 102-108 ohm m can be comminuted by the present device.
As stated this method of induced charging has been found to provide better comminution of liquid having a lower electrical resistivity, such as is the case of aqueous solvents, including solvent mixtures, and solutions thereof and low resistivity organic solvents such as alcohols.
One favoured use of the device of the invention is for the dispensation of a comminuted liquid for inhalation.
Accordingly, in one preferred aspect of the invention there is provided a device for comminuting a liquid for inhalation, wherein the liquid is comminuted by an induced electrical charge.
The device of the invention may be adapted into any embodiment form which dispenses comminuted liquid for inhalation, for both medicinal and non-medicinal use.
Non-medicinal inhalation uses includes dispensing perfumes and aromas.
Preferably, the device is in the form of an inhaler, for the inhaler delivery of a medicament.
A preferred liquid is therefore a liquid medicament formulation adapted for inhaled administration.
Medicaments suitable for adaption for inhaled administration include those used for the treatment of disorders of the respiratory tract, such as reversible airways obstruction and asthma and those used in the treatment and/or prophylaxis of disorders associated with pulmonary hypertension and of disorders associated with right heart failure by inhaled delivery.
One problem associated with inhalers it coordinating the release of the liquid spray with inhalation by the user. It is a further aspect of the present invention that there is provided a means which facilitates this problem.
Accordingly, there is also provided an inhaler, comprising an electrohydrodynamic comminution means, a means for partially or fully discharging the liquid comminution and a conduit through which the liquid comminution is administered, wherein the discharging means is arranged to be activated by inhalation of the user.
Suitably, the electrohydrodynamic comminution means comprises a communition site and a charging means, the charging means acting directly or by induction to product the required charge on the communition means, favourably acting by induction.
Suitably, the electrohydrodynamic communition means comprises a means for supplying liquid to the communition means.
One favoured arrangement wherein the discharging means is activated by inhalation of the user comprises a valve means located so as to open and close the conduit, suitably within the conduit, the valve means being opened by inhalation of the user which then activates the discharging means.
A suitable discharging means is provided by one or more capacitors or by a sharp edged or pointed electrode.
When the discharging means is a sharp edged or pointed electrode, the discharging means is preferably operationally attached to the valve means such that when the valve means opens the sharp edged or pointed electrode is thereby exposed to the communited liquid.
A suitable valve means is a flap valve.
In a particular instance the sharp edged or pointed electrode is fixed so as to extend upwards from the plane of the flap valve, the flap valve being pivotally fixed so as to open and close the conduit, such that when the flap valve pivots open the sharp edged or pointed electrode pivots into the flight path of the comminuted liquid.
Thus in a most particular instance the invention provides an inhaler, the inhaler comprising an electrohydrodynamic comminution site, a means for supplying liquid to the comminution site, a means for charging the comminution site, a sharp edged or pointed electrode for partially or fully discharging the liquid comminution and a conduit through which the liquid comminution is administered, the conduit having a valve means activated by inhalation of the user, wherein the valve means comprises a flap shaped to seal the conduit, the flap being pivotally fixed so as to open and close the conduit, the sharp edged or pointed electrode extends upwards from the plane of the flap valve, such that in the use the flap valve pivots open and the discharging means pivots into the flight path of the comminuted liquid.
When the devices comprise a sharp edged or pointed electrode, the arrangement suitably provides that the sharp edged or pointed electrode is electrically shielded from the liquid comminution when the valve means is closed. One particular method of achieving this is that the sharp edged or pointed electrode pivots into a recess formed in the charging means when the valve means closes.
When used herein xe2x80x98a comminutionxe2x80x99 includes a liquid droplet spray.
When used herein xe2x80x98medicamentxe2x80x99 includes proprietary medicines, pharmaceutical medicines and veterinary medicines.
When used herein, unless more specifically defined herein, xe2x80x98inhaled administrationxe2x80x99 includes administration to and via the upper respiratory tract, including the nasal mucosa, and the lower respiratory tract.
The description xe2x80x98sharp edged or pointedxe2x80x99 when used herein in relation to operational parts of the device, such as the electrode, also includes electrical equivalents thereof and hence includes shapes such as ridges and the like: The essential requirements is that the operational part of the device has, or a component or feature of the device has, dimensions which will give rise to a sufficiently high electrical field strength so as to exceed the breakdown strength of the air. This topic is theoretically described in xe2x80x9cDepositional Control of Macroscopic Particles by High Strength Electric Field Propulsionxe2x80x9d by R A Coffee, in xe2x80x9cTransactions of the Institution of Electrical and Electronic Engineers, Industry Applications, USAxe2x80x9d, Vol. IA-10 pp 511 to 519, July/August 1974. An example is an electrical field strength of approximately 3 million volts per meter.
The liquid medicinal formulations for use in the device of the invention may be formulated according to conventional procedures, such as those disclosed in the US Pharmacopoeia, the European Pharmacopoeia, 2nd Edition, Martindale The Extra Pharmacopoeia, 29th Edition, Pharmaceutical Press and the Veterinary Pharmacopoeia.
The liquid cosmetic formulations for use in the device of the invention may be formulated according to conventional procedures, such as those disclosed in Harry""s Cosemticology, 9th Edition, 1982, George Goodwin, London.